Campbell et al. (2004) used the detection algorithm method to study sales of cough, cold, sinus, and allergy products during outbreaks of respiratory diseases. They used the detection algorithm method to assess the lead time of sales of these products relative to a gold standard formed from billing data from physician office visits. They studied ten major U.S. cities for a period of three years (2000-2002). Similar to Hogan and colleagues, they formed time series by aggregating the OTC sales data into weekly counts for each of eight OTC product categories (adult and pediatric versions of cough, cold, sinus, and allergy). They formed gold-standard reference time series by aggregating the billing data (which comprised 22.5 million anonymized records corresponding to visits with respiratory-related ICD-9 codes for the 10 cities during the 2000-2002 period) into weekly counts.
They identified the beginning of the seasonal rise of respiratory ICD9 codes by inspection for each year and for each city. This method identified a total of 30 outbreaks for study. They used several simple detection algorithms (such as autoregression) to identify the first date of detection from both the OTC and office visit time series.
They found that for a number of categories (with the notable exception of allergy medications), detection of seasonal outbreaks of respiratory disease from OTC sales preceded detection from physician office visits. The lead time for the best categories (sinus and pediatric cough) was one to seven days.
Ohkusa et al. (2005) used correlation analysis to study the relationship between sales of OTC cold remedies and influenza activity in Japan. They found a poor correlation, with the adjusted r2 never rising above 0.50. However, they performed the analysis at the national level with respect to geography, as opposed to other studies discussed in this chapter, which analyzed data at the metropolitan level. Also, the study included herbal remedies in the cold remedy category, a type of medication not included in other analyses. Finally, the authors caution that their results are preliminary, and that they plan to conduct additional analyses.
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